P1651R0 bind_front should not unwrap reference_wrapper

P1651R0 bind_front should not unwrap reference_wrapper
	* include/std/functional (bind_front): Don't unwrap reference_wrapper.
	* include/std/version (__cpp_lib_bind_front): Update value.
	* testsuite/20_util/function_objects/bind_front/1.cc: Fix test for
	feature test macro.
	* testsuite/20_util/function_objects/bind_front/2.cc: New test.

From-SVN: r274146

libstdc++-v3/ChangeLog

@@ -1,5 +1,12 @@
 2019-08-06  Jonathan Wakely  <jwakely@redhat.com>
 
+	P1651R0 bind_front should not unwrap reference_wrapper
+	* include/std/functional (bind_front): Don't unwrap reference_wrapper.
+	* include/std/version (__cpp_lib_bind_front): Update value.
+	* testsuite/20_util/function_objects/bind_front/1.cc: Fix test for
+	feature test macro.
+	* testsuite/20_util/function_objects/bind_front/2.cc: New test.
+
 	* include/std/numbers [!__STRICT_ANSI__ && _GLIBCXX_USE_FLOAT128]
 	(e_v, log2e_v, log10e_v, pi_v, inv_pi_v, inv_sqrtpi_v, ln2_v, ln10_v)
 	(sqrt2_v, sqrt3_v, inv_sqrt3, egamma_v, phi_v): Add explicit

libstdc++-v3/include/std/functional

@@ -791,7 +791,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
 #if __cplusplus > 201703L
-#define __cpp_lib_bind_front 201902L
+#define __cpp_lib_bind_front 201907L
 
   template<typename _Fd, typename... _BoundArgs>
     struct _Bind_front
@@ -877,7 +877,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _Fn, typename... _Args>
     using _Bind_front_t
-      = _Bind_front<decay_t<_Fn>, unwrap_ref_decay_t<_Args>...>;
+      = _Bind_front<decay_t<_Fn>, decay_t<_Args>...>;
 
   template<typename _Fn, typename... _Args>
     _Bind_front_t<_Fn, _Args...>

libstdc++-v3/include/std/version

@@ -151,7 +151,7 @@
 #if __cplusplus > 201703L
 // c++2a
 #define __cpp_lib_atomic_ref 201806L
-#define __cpp_lib_bind_front 201902L
+#define __cpp_lib_bind_front 201907L
 #define __cpp_lib_bounded_array_traits 201902L
 #if __cpp_impl_destroying_delete
 # define __cpp_lib_destroying_delete 201806L

libstdc++-v3/testsuite/20_util/function_objects/bind_front/1.cc

@@ -23,7 +23,7 @@
 
 #ifndef __cpp_lib_bind_front
 # error "Feature test macro for bind_front is missing"
-#elif __cpp_lib_bind_front < 201811L
+#elif __cpp_lib_bind_front < 201902L
 # error "Feature test macro for bind_front has wrong value"
 #endif
 

libstdc++-v3/testsuite/20_util/function_objects/bind_front/2.cc

@@ -0,0 +1,91 @@
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <functional>
+#include <memory>
+#include <string>
+#include <testsuite_hooks.h>
+
+// P1651R0 bind_front should not unwrap reference_wrapper
+
+#ifndef __cpp_lib_bind_front
+# error "Feature test macro for bind_front is missing"
+#elif __cpp_lib_bind_front < 201907L
+# error "Feature test macro for bind_front has wrong value"
+#endif
+
+void functionAcceptingStringView(std::string_view) { }
+
+void
+test01()
+{
+  std::string s;
+  auto fs = std::bind_front(&functionAcceptingStringView, std::string_view(s));
+  fs();
+}
+
+template <typename F>
+struct PartialApply {
+    PartialApply(F f) : f(f) {}
+    F f;
+
+    template <typename... A> decltype(auto) operator()(A const&... a) const {
+        if constexpr (std::is_invocable<F const&, A const&...>::value) {
+            return f(a...);
+        } else {
+            return bind_front(*this, a...);
+        }
+    }
+};
+
+void
+test02()
+{
+  struct Thingy { };
+  std::unique_ptr<Thingy> thingy;
+  auto func = [](const std::unique_ptr<Thingy>&, int) {};
+  PartialApply{func}(std::ref(thingy))(10);
+}
+
+void
+test03()
+{
+  std::string str;
+  auto func = [](const std::string& s, int) -> const std::string& { return s; };
+
+  // sref refers to copy of str stored in bind_front result:
+  const std::string& sref = PartialApply{func}(std::ref(str))(10);
+
+  // pre-P1651R0 this is a use of a dangling reference:
+  const char& c = sref[0];
+
+  // post-P1651R0 the bind_front result stores a reference_wrapper by value,
+  // and so sref is bound to str instead of dangling:
+  VERIFY( &c == str.data() );
+  VERIFY( &sref == &str );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+}